[PATCH] branch: avoid slow strvec Coccinelle matching

[PATCH] branch: avoid slow strvec Coccinelle matching

[tnyman]

From: Ted Nyman <tnyman@openai.com>

The --delete-merged implementation declares a loop index at function
scope and reuses it to walk its strvec of upstreams and its list of
candidate branches. Coccinelle 1.1.1 spends hours matching this against
the separate_loop_index rule in tools/coccinelle/strvec.cocci, causing
the static-analysis job on 'seen' to reach its six-hour timeout.

Declare each index in its for loop instead. This avoids the expensive
separate-index rule, limits each index to the loop that uses it, and
leaves the branch deletion behavior unchanged.

Signed-off-by: Ted Nyman <tnyman@openai.com>
---
This applies on top of hn/branch-delete-merged and addresses the long
static-analysis runs on 'seen'. Coccinelle 1.1.1 spends hours matching
the existing separate_loop_index rule against delete_merged_branches().

Declare each loop index in its for statement instead of sharing an
index declared at function scope. This avoids the pathological matching
without changing branch behavior.

The CI failure reproduces locally with Coccinelle 1.1.1: applying
strvec.cocci to the original builtin/branch.c still times out with
"spatch --timeout 120". With this change, the same check completes in
0.06 seconds.

The full coccicheck run completes in 47 seconds, and all 190 tests in
t3200-branch.sh pass with a fresh DEVELOPER=1 build.

 builtin/branch.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/builtin/branch.c b/builtin/branch.c
index 42f2221547..2415a275ea 100644
--- a/builtin/branch.c
+++ b/builtin/branch.c
@@ -797,10 +797,9 @@ static int delete_merged_branches(const struct strvec *upstreams,
 	struct strbuf key = STRBUF_INIT;
 	struct hashmap_iter iter;
 	struct strmap_entry *entry;
-	size_t i;
 	int ret = 0;
 
-	for (i = 0; i < upstreams->nr; i++)
+	for (size_t i = 0; i < upstreams->nr; i++)
 		if (ref_filter_forked_add(&filter, upstreams->v[i]) < 0)
 			die(_("'%s' is not a valid branch or pattern"),
 			    upstreams->v[i]);
@@ -809,7 +808,7 @@ static int delete_merged_branches(const struct strvec *upstreams,
 	filter.name_patterns = argv;
 	filter_refs(&candidates, &filter, filter.kind);
 
-	for (i = 0; i < (size_t)candidates.nr; i++) {
+	for (size_t i = 0; i < (size_t)candidates.nr; i++) {
 		const char *branch_refname = candidates.items[i]->refname;
 		const char *branch_name;
 		struct branch *branch;
-- 
2.54.0.8.g047e0526de

Re: [PATCH] branch: avoid slow strvec Coccinelle matching

[Jeff King]

On Fri, Jul 24, 2026 at 02:11:53AM -0700, tnyman@openai.com wrote:

> The --delete-merged implementation declares a loop index at function
> scope and reuses it to walk its strvec of upstreams and its list of
> candidate branches. Coccinelle 1.1.1 spends hours matching this against
> the separate_loop_index rule in tools/coccinelle/strvec.cocci, causing
> the static-analysis job on 'seen' to reach its six-hour timeout.

Yuck. So this is really a coccinelle problem. It looks like it has been
fixed (or at least improved) in recent versions. I can reproduce the
slowness locally on 1.2.0 (I couldn't get 1.1.1 to build), but 1.3.0 is
fast. Bisection turns up 58619b8fe (break up envs for e1 & e2,
2024-08-18), which says:

    Since 362937b2a84840e68ae021171df10c7a4cc6fbef, e1 ... e2 has the
    quantifiers for the free variables of e1 around the whole thing, to ensure
    that the when code on the ... refers to the same variables as e1.  This can
    make the semantic patch very slow, as illustrated by kmerr.cocci in
    scripts/coccinelle/null/kmerr.cocci in the Linux kernel.  The slowness
    comes from environments based on multipl metavariable bindings getting very
    large.

    To reduce (but not solve) the problem, for the first & where the left side
    has multiple results, consider these results individually when working on
    the right side, and then union the results.  This may lead to some loss of
    sharing.  Maybe it is not advantageous when the ... contains when any and
    does not contain any explicit when clause containing the variables of e1.

The static-analysis CI job uses the ubuntu-22.04 image, for no reason
that I can really discern. It looks like coccinelle 1.3.0 is in ubuntu
25.10, according to:

  https://packages.ubuntu.com/km/questing/coccinelle

Why don't we just use the more recent version instead of trying to work
around it? That would fix this problem and prevent future ones. Looking
at the code in question:

> diff --git a/builtin/branch.c b/builtin/branch.c
> index 42f2221547..2415a275ea 100644
> --- a/builtin/branch.c
> +++ b/builtin/branch.c
> @@ -797,10 +797,9 @@ static int delete_merged_branches(const struct strvec *upstreams,
>  	struct strbuf key = STRBUF_INIT;
>  	struct hashmap_iter iter;
>  	struct strmap_entry *entry;
> -	size_t i;
>  	int ret = 0;
>  
> -	for (i = 0; i < upstreams->nr; i++)
> +	for (size_t i = 0; i < upstreams->nr; i++)
>  		if (ref_filter_forked_add(&filter, upstreams->v[i]) < 0)
>  			die(_("'%s' is not a valid branch or pattern"),
>  			    upstreams->v[i]);

...there is nothing suspicious or wrong about it. It seems likely that
somebody else may end up writing something similar and triggering the
same problem.

That said, moving the iterator into the loop declaration is perhaps
nicer anyway, because it avoids two unrelated uses of the same variable.
Notably:

> @@ -809,7 +808,7 @@ static int delete_merged_branches(const struct strvec *upstreams,
>  	filter.name_patterns = argv;
>  	filter_refs(&candidates, &filter, filter.kind);
>  
> -	for (i = 0; i < (size_t)candidates.nr; i++) {
> +	for (size_t i = 0; i < (size_t)candidates.nr; i++) {
>  		const char *branch_refname = candidates.items[i]->refname;
>  		const char *branch_name;
>  		struct branch *branch;

This hunk is not using a strvec at all. Because it uses the same
variable, if we did not change this loop, then we'd still have to
declare "i" at the top of the function and the other loop would
introduce a shadowed variable. That's not wrong, but it is confusing.

However, if we are going to have our own variable here, perhaps it
should use the correct type? candidate.nr is an int, so probably this
should also be an int, and then the gross cast can go away.

-Peff

Re: [PATCH] branch: avoid slow strvec Coccinelle matching

[Harald Nordgren]

Thanks for the report, Ted! CI had been timing out on this branch, but
I chalked it up to one of the many CI failures we had in the last few
months. CI is now generally stable again for some days, and with your
fix it's also green on this branch specifically.

Good point, Jeff, probably it can be 'int i' in the 'candidates.nr',
case to avoid a cast. I'll push it to GitHub to verify that the CI
passes there as well, but I'll wait with submitting until others have
finished reviewing, to not overload inboxes after already pushing out
one version today.


Harald

Re: [PATCH] branch: avoid slow strvec Coccinelle matching

[Junio C Hamano]

tnyman@openai.com writes:

> From: Ted Nyman <tnyman@openai.com>
>
> The --delete-merged implementation declares a loop index at function
> scope and reuses it to walk its strvec of upstreams and its list of
> candidate branches. Coccinelle 1.1.1 spends hours matching this against
> the separate_loop_index rule in tools/coccinelle/strvec.cocci, causing
> the static-analysis job on 'seen' to reach its six-hour timeout.
> ...
> The CI failure reproduces locally with Coccinelle 1.1.1: applying
> strvec.cocci to the original builtin/branch.c still times out with
> "spatch --timeout 120". With this change, the same check completes in
> 0.06 seconds.

Impressive.  Nicely analyzed.

Even though this is very much like bending the code only to appease
the checker, the resulting code is arguably better in this
particular case, so I do not feel as bad as I have on other
occasions when we had to work around deficiencies in our tools [*].

I see Harald already took this in the latest update.  Thanks for
working well together.

[*]

 * Here, I do not blame Coccinelle alone.  The performance bug is
   caused by a combination of Coccinelle and the 'strvec' check that
   makes it so inefficient.  I wonder if there are ways to make the
   checks in 'strvec.cocci' more efficient?


> diff --git a/builtin/branch.c b/builtin/branch.c
> index 42f2221547..2415a275ea 100644
> --- a/builtin/branch.c
> +++ b/builtin/branch.c
> @@ -797,10 +797,9 @@ static int delete_merged_branches(const struct strvec *upstreams,
>  	struct strbuf key = STRBUF_INIT;
>  	struct hashmap_iter iter;
>  	struct strmap_entry *entry;
> -	size_t i;
>  	int ret = 0;
>  
> -	for (i = 0; i < upstreams->nr; i++)
> +	for (size_t i = 0; i < upstreams->nr; i++)
>  		if (ref_filter_forked_add(&filter, upstreams->v[i]) < 0)
>  			die(_("'%s' is not a valid branch or pattern"),
>  			    upstreams->v[i]);
> @@ -809,7 +808,7 @@ static int delete_merged_branches(const struct strvec *upstreams,
>  	filter.name_patterns = argv;
>  	filter_refs(&candidates, &filter, filter.kind);
>  
> -	for (i = 0; i < (size_t)candidates.nr; i++) {
> +	for (size_t i = 0; i < (size_t)candidates.nr; i++) {
>  		const char *branch_refname = candidates.items[i]->refname;
>  		const char *branch_name;
>  		struct branch *branch;

Re: [PATCH] branch: avoid slow strvec Coccinelle matching

[Junio C Hamano]

Jeff King <peff@peff.net> writes:

> The static-analysis CI job uses the ubuntu-22.04 image, for no reason
> that I can really discern. It looks like coccinelle 1.3.0 is in ubuntu
> 25.10, according to:
>
>   https://packages.ubuntu.com/km/questing/coccinelle
>
> Why don't we just use the more recent version instead of trying to work
> around it? That would fix this problem and prevent future ones. Looking
> at the code in question:
>
>> diff --git a/builtin/branch.c b/builtin/branch.c
>> index 42f2221547..2415a275ea 100644
>> --- a/builtin/branch.c
>> +++ b/builtin/branch.c
>> @@ -797,10 +797,9 @@ static int delete_merged_branches(const struct strvec *upstreams,
>>  	struct strbuf key = STRBUF_INIT;
>>  	struct hashmap_iter iter;
>>  	struct strmap_entry *entry;
>> -	size_t i;
>>  	int ret = 0;
>>  
>> -	for (i = 0; i < upstreams->nr; i++)
>> +	for (size_t i = 0; i < upstreams->nr; i++)
>>  		if (ref_filter_forked_add(&filter, upstreams->v[i]) < 0)
>>  			die(_("'%s' is not a valid branch or pattern"),
>>  			    upstreams->v[i]);
>
> ...there is nothing suspicious or wrong about it. It seems likely that
> somebody else may end up writing something similar and triggering the
> same problem.

Exactly.

> That said, moving the iterator into the loop declaration is perhaps
> nicer anyway, because it avoids two unrelated uses of the same variable.

Exactly again.

> Notably:
>
>> @@ -809,7 +808,7 @@ static int delete_merged_branches(const struct strvec *upstreams,
>>  	filter.name_patterns = argv;
>>  	filter_refs(&candidates, &filter, filter.kind);
>>  
>> -	for (i = 0; i < (size_t)candidates.nr; i++) {
>> +	for (size_t i = 0; i < (size_t)candidates.nr; i++) {
>>  		const char *branch_refname = candidates.items[i]->refname;
>>  		const char *branch_name;
>>  		struct branch *branch;
>
> This hunk is not using a strvec at all. Because it uses the same
> variable, if we did not change this loop, then we'd still have to
> declare "i" at the top of the function and the other loop would
> introduce a shadowed variable. That's not wrong, but it is confusing.
>
> However, if we are going to have our own variable here, perhaps it
> should use the correct type? candidate.nr is an int, so probably this
> should also be an int, and then the gross cast can go away.

Ah, very good eyes.  It is a disease to try appeasing -Wsign-compare
without thinking, instead of questioning the value of the warning
first, and in this case there is no reason to try forcing the use of
size_t, even with the unnecessary casting.

Re: [PATCH] branch: avoid slow strvec Coccinelle matching

[Junio C Hamano]

Junio C Hamano <gitster@pobox.com> writes:

>> Notably:
>>
>>> @@ -809,7 +808,7 @@ static int delete_merged_branches(const struct strvec *upstreams,
>>>  	filter.name_patterns = argv;
>>>  	filter_refs(&candidates, &filter, filter.kind);
>>>  
>>> -	for (i = 0; i < (size_t)candidates.nr; i++) {
>>> +	for (size_t i = 0; i < (size_t)candidates.nr; i++) {
>>>  		const char *branch_refname = candidates.items[i]->refname;
>>>  		const char *branch_name;
>>>  		struct branch *branch;
>>
>> This hunk is not using a strvec at all. Because it uses the same
>> variable, if we did not change this loop, then we'd still have to
>> declare "i" at the top of the function and the other loop would
>> introduce a shadowed variable. That's not wrong, but it is confusing.
>>
>> However, if we are going to have our own variable here, perhaps it
>> should use the correct type? candidate.nr is an int, so probably this
>> should also be an int, and then the gross cast can go away.
>
> Ah, very good eyes.  It is a disease to try appeasing -Wsign-compare
> without thinking, instead of questioning the value of the warning
> first, and in this case there is no reason to try forcing the use of
> size_t, even with the unnecessary casting.

Having said that, another fix might be to standardize the way we
count the number of things in an array and update 'ref-filter.h' to
use size_t in 'struct ref_array' as well.

It is not as though 2 billion refs are too few to satisfy our
needs, and in general, the platform-natural int should be used to
count things unless there is a compelling reason to deviate from
that norm.  However, "somehow we ended up counting many things in
size_t, so it is better to count everything using the same type"
could serve as "the compelling reason" to make such a change.

Re: [PATCH] branch: avoid slow strvec Coccinelle matching

[Junio C Hamano]

Junio C Hamano <gitster@pobox.com> writes:

>> Ah, very good eyes.  It is a disease to try appeasing -Wsign-compare
>> without thinking, instead of questioning the value of the warning
>> first, and in this case there is no reason to try forcing the use of
>> size_t, even with the unnecessary casting.
>
> Having said that, another fix might be to standardize the way we
> count the number of things in an array and update 'ref-filter.h' to
> use size_t in 'struct ref_array' as well.
>
> It is not as though 2 billion refs are too few to satisfy our
> needs, and in general, the platform-natural int should be used to
> count things unless there is a compelling reason to deviate from
> that norm.  However, "somehow we ended up counting many things in
> size_t, so it is better to count everything using the same type"
> could serve as "the compelling reason" to make such a change.

Let's not allow too much latitude to ourselves, as that would only
confuse us.

Here is what I recommend that we do.  In the short term, i.e.,
within the context of the topic in question, let's use 'int' to
match the type used to count the members of an array embedded in
'struct ref_array'.

But let's leave a '#leftoverbits' note here in the mailing list
archive to remind us to revisit the idea of consistently using
'size_t' to count things when things are quiet.  This is not the
time to needlessly disrupt the 'hn/branch-delete-merged' topic, I
think.

Re: [PATCH] branch: avoid slow strvec Coccinelle matching

[Taylor Blau]

On Fri, Jul 24, 2026 at 08:27:06AM -0700, Junio C Hamano wrote:
> tnyman@openai.com writes:
>
> > From: Ted Nyman <tnyman@openai.com>
> >
> > The --delete-merged implementation declares a loop index at function
> > scope and reuses it to walk its strvec of upstreams and its list of
> > candidate branches. Coccinelle 1.1.1 spends hours matching this against
> > the separate_loop_index rule in tools/coccinelle/strvec.cocci, causing
> > the static-analysis job on 'seen' to reach its six-hour timeout.
> > ...
> > The CI failure reproduces locally with Coccinelle 1.1.1: applying
> > strvec.cocci to the original builtin/branch.c still times out with
> > "spatch --timeout 120". With this change, the same check completes in
> > 0.06 seconds.
>
> Impressive.  Nicely analyzed.
>
> Even though this is very much like bending the code only to appease
> the checker, the resulting code is arguably better in this
> particular case, so I do not feel as bad as I have on other
> occasions when we had to work around deficiencies in our tools [*].

Agreed. I don't think we should ever bend over backwards to appease a
static analysis tool, *especially* when it results in worse looking
code. But this case is a strict improvement, and just so happens to
address the Coccinelle issue. ;-)

> I see Harald already took this in the latest update.  Thanks for
> working well together.

Yup. Thanks, both.

Thanks,
Taylor